When you and your period hit perimenopause, “go with the flow” can take on a whole new meaning.

Your period flow may stay regular for a while, but if you’re like many women, it might also seem to take on a mind of its own. Most women start perimenopause in their 40's, but for some, skipped cycles and period irregularities (like a heavier flow, which affects nearly 1/3 of those in perimenopause) may begin in their late 30s. This can be  normal, and often not cause for concern—but you do want to stay aware.

Let’s look at some of the ways perimenopause may change your flow and when it may be time to call the doc.

Your period flow may become heavier

In perimenopause, heavy periods can be common—oh, joy, right? Fluctuating hormones are typically to blame: When your estrogen levels are higher compared to your progesterone levels and the balance gets out of whack, your uterine lining thickens—so, when your period starts and your lining sheds, that’s going to mean more bleeding.

It’s also more common during perimenopause to skip a period, which means your uterine lining will continue to build until your next period—and again, the more uterine lining you have to shed, the heavier the bleeding.

What classifies as “heavy” bleeding? Watch for these signs, according to the CDC:

• You soak through one or more pads or tampons every hour for several hours in a row.
• You need to double up on pads, or use a pad and a tampon together, to control your flow.
• You need to change pads or tampons during the night.
• You bleed for more than 7 days.
• Your flow includes blood clots the size of a quarter or larger..

It may seem alarming to bleed this much, especially if your periods have tended to be on the light side. While heavy periods are a common perimenopause symptom, it’s always advised to check with your healthcare provider if you have a significant change in bleeding patterns as this change can be a sign of a more serious condition.

Your flow may change colors

By the time you reach your 40s, you’re used to seeing bright red period blood—but what about brown? What the heck is brown blood doing in your period?! Two words: Hormonal imbalance. Here’s what happens: Our old pal, estrogen, maintains the lining of our uterus. When it plunges, that’s when the lining leaves your body and you start bleeding. During perimenopause, estrogen levels can bounce around a bit, so your uterine lining may break down at different times without being expelled. If it hangs out in your uterus for a while, it turns brown. Basically, brown blood equals “old” blood. 

Should you ever be concerned about brown blood? Call your doc if it smells bad, it lasts a long time (several weeks), or you’re running a fever and/or feeling pain.

Your flow may get lighter and/or irregular

When estrogen levels fluctuate, as they do when you begin perimenopause, you may have  shorter and lighter periods. Shorter cycles can be common in early perimenopause, coming maybe every 2-3 weeks and lasting just a few days. In fact, this can be one of the first signs that your estrogen levels are starting to change. That said, if your flow is suddenly so light that a tampon is uncomfortable, you’ll want to check in with a healthcare provider.

You may have cramping, but no actual period

This can be really confusing! But hang on for a second—we’ll explain. While it’s true that your estrogen levels typically decrease during perimenopause, this doesn’t happen in a perfectly linear fashion. Sometimes, your estrogen might unexpectedly surge. Your ovaries are still like, “Must produce more mature eggs,” so your body pumps out more follicle stimulating hormone (FSH). This not only increases estrogen, but it also raises your levels of prostaglandins—hormones responsible for the uterine contractions that make you want to crawl in bed with a heating pad and tub of ice cream.

While those hormones are raging, progesterone—a hormone that triggers your period to start—is basically on the decline. Erratic hormone patterns may mean that some months you may not experience a period flow, but you might still have cramps and other PMS symptoms. 

Remember, most changes in your period or flow during your 40s are likely due to perimenopause. This may feel unsettling, especially if you’ve been regular for years. It’s extremely important to talk to your healthcare provider if something seems truly off (too much bleeding or periods consistently occurring less than every 3 weeks, for example), but it’s likely that changing hormone levels are most likely what’s behind your period’s erratic behavior.